Level control assemblies of the generally described kind are known in which, in a predetermined position of the working piston, after the control opening has been opened by displacement of the piston rod, the oil can flow from the high pressure chamber by way of the control opening directly to the low pressure chamber. A disadvantageous effect in that arrangement is that when the control opening is opened for a short period of time, the pressure is reduced in a short time. A reduction in pressure in a short time in that way occurs, for example, after the vehicle has taken a curve at high speed, or after heavy braking in which the rear of the vehicle rises. The undesired change in the positional level under these circumstances gives rise to disadvantageous effects on the performance and road holding of the vehicle. For examples of such known devices, see German Pat. No. 1,630,107, U.S. Pat. No. 3,497,199, U.S. Pat. No. 4,368,878, and commonly assigned U.S. Pat. No. 4,502,672.
Level control arrangements are also known (for example, German laid-open application (DE/OS) No. 3020050) which use a plurality of control openings operating in conjunction with a conical or tapered piston rod. In an effort to provide a suitably delayed pressure reduction time, it is not possible to reduce the diameters of the control openings to just any value that may be desired, since, with openings of less than a given diameter, there is the danger that impurities in the oil may jam in the control opening and thus adversely affect the adjust-down performance.
With the foregoing as the basic starting point, an object of the present invention is to provide a simple, operationally reliable and relatively insensitive level control arrangement, in which the adjust-down time is increased so as to avoid undesired alterations in positional level, even when, for instance, the vehicle is taking a curve and/or experiencing heavy braking.
According to the invention, that object is attained in that disposed in the pump rod is a sleeve which connects the control opening to the bore in the pump rod by way of a connecting duct and a throttle means, the sleeve optionally functioning as or as part of the throttling arrangement. An advantage with this arrangement is that the sleeve provides a duct for the oil flowing from the control opening to the pump rod bore. The sleeve, which itself serves to effect a delay action, prevents the oil from flowing directly from the high pressure chamber into the lower pressure chamber so that the control opening no longer need operate as a throttle, but rather throttle means of various configurations may be utilized as a time delay means. For that reason, it is possible for the diameter of the control opening to be increased, while the danger of a blockage due to impurities in the oil is reduced. With this control feature, on the one hand, the control opening is rendered less fine for harsh vehicle operating conditions, and at the same time a relatively insensitive control component or feature is provided, while, on the other hand, the arrangement provides an adjust-down time which has a time delay.
In accordance with a particularly preferred embodiment, the throttle means cooperates with the suction valve located at one end of the pump rod bore.
In accordance with an advantageous feature, the throttle means is disposed in the end surface of the sleeve and has at least one opening, and the remaining end surface of the sleeve serves as an abutment surface for the valve plate of the suction valve. That arrangement eliminates the disadvantages of a blockage of the opening as, during subsequent actuation of the suction valve, the valve plate lifts away from the end surface of the sleeve and the pump rod so that the oil flowing therepast can flush away the pieces causing a blockage. That arrangement therefore provides a self-cleaning effect, and ensures that any blockage can only last for a short period of time. It is advantageously also possible for a wedge-shaped depression to be provided as the opening, and such a depression can be easily produced by a non-cutting production operation.
In accordance with a preferred embodiment of the invention, the suction valve has a valve plate which is supported on the end surface of the pump rod and which bends, under a prestress, and which, together with the end surface of the sleeve that is disposed at a spacing, forms the throttle means. That embodiment provides a load-dependent or pressure-dependent delay, by virtue of the use of a sleeve having an end surface of a given value under the operative surface area of the suction valve. A variable pressure-dependent throttle cross section is formed by virtue of different degrees of bending of the resilient spring plate at different pressures, thus varying the throttle passage between the sleeve and the resilient spring plate.
Additionally, delays in the adjust-down control action may be achieved by the connecting duct being in the form of a throttle means and having a predetermined throttle cross section over at least a part of its length. The throttle cross section may be formed by using a suitable annular gap between the inside diameter of the pump rod and the outside diameter of the sleeve.
Another advantageous possible feature provides that, to act as the throttle means, the connecting duct may be arranged to extend in a helical configuration on the outside surface of the sleeve or the inside surface of the pump rod. It is advantageous in that arrangement for the length and the cross section to correspond to the value to be throttled. By virtue of this configuration of the connecting duct, the oil flow is delayed so that the desired throttling value is achieved by virtue of a suitable selection in respect of the cross section and the length of the groove.
In all embodiments of the invention, the advantages of the invention are achieved in fundamentally the same manner, in that an undesired alteration in positional level can be achieved by a throttled control action producing a drop in pressure.
Other features and advantages of the invention will become apparent to those skilled in the art from the ensuing description of preferred embodiments taken in conjunction with the appended drawings.